Fix bug in formula criteria with only one condition

sfdx-source/apex-extensions/main/default/classes/criteria/fflib_Criteria.cls

@@ -248,11 +248,11 @@ public virtual with sharing class fflib_Criteria
 			for (IFormulaEvaluator evaluator : formulaParts)
 			{
 				Boolean evaluateResult = evaluator.evaluate(record, evaluatedResultByNumber);
-				if (evaluateResult && (this.type == 'OR'))
+				if (evaluateResult && (this.type == 'OR' || this.type == null))
 				{
 					return true;
 				}
-				else if (!evaluateResult && this.type == 'AND')
+				else if (!evaluateResult && (this.type == 'AND' || this.type == null))
 				{
 					return false;
 				}

sfdx-source/apex-extensions/tests/classes/criteria/fflib_CriteriaTest.cls

@@ -598,4 +598,21 @@ private with sharing class fflib_CriteriaTest
 						.evaluate(record)
 		);
 	}
+
+	@IsTest
+	static void itShouldEvaluateFormula_WithSingleItem()
+	{
+		System.assert(
+				new fflib_Criteria()
+						.FormulaCriteria('1')
+						.equalTo(Contact.LastName, 'Smith')
+						.evaluate(new Contact(LastName = 'Smith'))
+		);
+		System.assertEquals(false,
+				new fflib_Criteria()
+						.FormulaCriteria('1')
+						.equalTo(Contact.LastName, 'Ford')
+						.evaluate(new Contact(LastName = 'Smith'))
+		);
+	}
 }